1. Field of the Invention
The present invention relates to a plasma display panel and the driving method thereof, and more particularly, to a plasma display panel, one of flat panel display devices, having improved electrical connections and the driving method thereof.
2. Description of the Related Art
Generally, to display an image on a flat panel display device, a matrix driving method is utilized. In this method, a pair of electrodes are sequentially selected among a plurality of scan electrodes arranged in the same horizontal direction as the scanning direction of a video signal and a plurality of address electrodes arranged in the vertical direction, and on the cross point of the pair of the electrodes, a video signal of a pixel can be displayed. In addition, two types of steps are required to display images on a flat panel display device. One step is an addressing step to sequentially address each one of pixels of the display panel, and the other one is a sustaining discharge step to display a video signal for a certain period of time at the corresponding pixel. In the plasma display panel, the two types of steps are carried out by selecting a pair of horizontal and vertical electrodes, and by establishing a negative glow discharge within a discharge space filled with a gas between the two electrodes. In other words, after a pair of scan electrodes and an address electrode are selected according to the sync pulses of a video signal, and a pulse voltage is impressed at least one of the electrodes to establish a gas discharge at the selected pixel, a pulse voltage is impressed across the scan electrodes to achieve a sustaining discharge, and therefore the video signal is transformed to a light signal and is displayed at the selected pixel.
The structural types of the plasma display panels are classified into a facing discharge type and a surface discharge type according to arrangement configurations of discharge electrodes, the driving types of the plasma display panels are classified into an AC driving type and a DC type according to whether the polarity of the voltage impressed for sustaining discharges is varying with the passage of time or not.
FIG. 1a shows a basic structure of a general DC type facing discharge plasma display panel, and FIG. 1b shows a basic structure of a general AC type surface discharge plasma display panel. As shown in FIGS. 1a and 1b, the DC type facing discharge plasma display panel, and the AC type surface discharge plasma display panel are respectively provided with discharge spaces 5 and 15 between front glass substrates 1 and 11 and back glass substrates 7 and 17. In the DC type plasma display panel, since a scan electrode 2 and an address electrode 6 are directly exposed to the discharge space 5, the flow of electrons supplied by a cathode is the energy source sustaining a discharge. In the AC type plasma display panel, since the scan electrodes 12 are embedded in a dielectric layer 13, they are electrically isolated from the discharge space 15. In this case, the discharge is sustained by the well-known wall charge effect. In addition, the AC type plasma display panels are classified into a facing discharge type and a surface discharge type according to the disposition of electrodes establishing discharges.
In the facing discharge plasma display panel, a pixel is addressed by the address electrode 6 on the back substrate 7 and the scan electrode 2 on the front substrate 1 which are disposed to face each other and to be orthogonal to each other and are addressed according to sync pulses of the video signal, and the discharge occurs and is sustained in the discharge space between the electrodes 2 and 6. In the surface discharge plasma display panel, a pair of the scan electrodes 12 formed on the front substrate 11 to be parallel to each other and the address electrode 16 formed on the back substrate 17 to be orthogonal with respect to the electrodes 2 and 6 are provided. In this panel, an address discharge occurs between the address electrode 16 and the scan electrodes 12, and then a sustaining discharge to display a video signal occurs between two scan electrodes 12, namely, an X electrodes 12a and an Y electrodes 12b. Further, each type may employ 3 electrode structure, 4 electrode structure and so on including a plurality of scan electrodes and/or address electrodes in order to easily establish the discharge.
FIG. 2 shows a schematic exploded perspective view of an AC type 3 electrode surface discharge plasma display panel which is commercially available. An address electrode 16 and a pair of scan electrodes 12 to be orthogonal with respect to the address electrode 16 are disposed at both sides of a corresponding point of a discharge space 15. Partition walls 18 have roles to define discharge spaces 15 and to prevent cross talks between neighbor pixels from occurring by blocking space charges created during a discharge period and ultraviolet rays. To make a plasma display panel capable of displaying color images as a color display device, fluorescent materials 19 which can be excited by ultraviolet rays radiated during a discharge period and respectively emit visible light rays of red, blue, and green colors are respectively coated on the inside surfaces of the discharge spaces sequentially and repeatedly.
Such a plasma display panel coated with the fluorescent materials has to exhibit gray scale to achieve a preferable performance of a color image display device, and a gray scale exhibition method in which a image frame is divided into a plurality of subfields and the panel is driven in a time-division manner is currently utilized. FIG. 3 shows a diagram to explain a gray scale exhibition method of a general AC type plasma display panel. As shown in FIG. 3, the gray scale exhibition method of the AC type plasma display panel employs a method in which a image frame is divided into 4 subfields operated in a time-division manner and 2.sup.4 =16 gray scale can be displayed. The operation period of each subfield consist of respective one of address periods A1 to A4 and respective one of sustaining discharge periods S1 to S4, the fact that the brightness perceived by human eyes is directly proportional to the relative duration of the sustaining discharge period is utilized to exhibit the gray scale. In other words, since the sustaining discharge periods S1 to S4 of a first subfield SF1 to a fourth subfield SF4 are in the ratio 1:2:4:8, combinational periods of each sustaining discharge period such as 0, 1 (1T), 2 (2T), 3 (1T+2T), 4 (4T), 5 (1T+4T), 6 (2T+4T), 7 (1T+2T+4T), 8 (8T), 9 (1T+8T), 10 (2T+8T), 11 (3T+8T), 12 (4T+8T), 13 (1T+4T+8T), 14 (2T+4T+8T), 15 (1T+2T+4T+8T) are possible and therefore 16 level gray scale can be displayed. For example, in order to display level 6 of the gray scale in a certain pixel, the second subfield 2T and the third subfield 4T have to be addressed, and in order to display level 15 of the gray scale, all of the first, second, third and fourth subfields have to be addressed.
FIG. 4 shows a diagram of an electrode connection scheme of an AC type 3 electrode surface discharge plasma display panel to realize the gray scale exhibition method as described above. As shown in FIG. 4, X electrodes 12a of scan electrodes 12 are connected to a common line, and accordingly a voltage signal of the same waveform including a sustaining discharge pulse is impressed to all the X electrodes 12a. Therefore, as a scan signal of the scan electrodes 12 is impressed to an Y electrode, an address discharge occurs between the Y electrode 12b and an address electrode 6, and then as a sustaining discharge pulse is impressed across the Y electrode 12b and the X electrodes, the display discharge is sustained. The waveforms of driving signals respectively impressed to the electrodes connected as described above are shown in FIG. 5.
In FIG. 5, A represents a driving signal to be impressed to each address electrode, X represents a driving signal to be impressed to each common electrode, i.e., X electrode 12a, and Y1 to Y480 represent driving signals respectively to be impressed to Y electrodes 12b. During a total erase period A11, in order to display an exact level of the gray scale, a total erase pulse 22a is impressed to the X electrode 12a to establish a strong discharge, and consequently a wall charge created by the previous discharge is erased, as shown in FIG. 6a, to make the following operation of subfields properly be carried out (the first step). During a total write period A12 and a total erase period A13, in order to lower an address pulse voltage, a total write pulse 23 is impressed to the Y electrode 12b and a total erase pulse 22b is impressed to the X electrode 12a to respectively establish a total write discharge and a total erase discharge, as shown in FIG. 6b and 6c, to control the amount of the wall charge within a charge space 15 (the second and third steps). During an address period A14, a selective charge by an address pulse (a data pulse) 21 across an address electrode 16 and the scan electrode 12b which are orthogonal with respect to each other effects an operation to write, as shown in FIG. 6d, electrically coded information at a selected position of the plasma display panel (the fourth step). During sustaining discharge period S1, a sustaining discharge by a continuous sustaining discharge pulse 25 sustains a display discharge for a given period to display image information on an actual panel.
As described above, in the driving method of the AC type plasma display panel the electrodes of which are connected as shown in FIG. 4, since independent signals are inputted respectively to the Y electrodes 12b and the address electrodes 16 for address discharges as described above and display discharges to display image signals, each electrode requires a separate driving circuit. For example, a plasma display panel having 640.times.480 pixels requires one X electrode driving circuit and 480 Y electrode driving circuits, a total of 481 driving circuits for the scan electrodes. Usually, the driving circuit consists of an integrated circuit device incorporated with electronic circuit devices having at least one switch, and the integrated circuit device is referred to as a driver IC. The driver IC requires a high voltage due to the discharge characteristics, and especially since driver ICs used in the X and Y electrodes for display discharges requires a high voltage of about 200V, it is required to use driver ICs of a very high price. Currently, since the price of the driving circuit portion forms a great part of the total cost of a plasma display panel, it is a decisive obstacles in the commercial success of the plasma display panel. To enhance the marketability of the plasma display panel, it is most important that the number of the driving circuit devices is reduced to lower the cost and the power consumption of the plasma display panel.